In the manufacture and testing of small electronic parts, such as integrated circuits which are sold in packages having dimensions of two inches or less, it is increasingly important to test such parts at high speed in order to keep up with the production rates of such parts.
Such small electronic parts, such as integrated circuits at first were packaged in dual-in-line packages (DIPs), which are small, elongated plastic boxes with the leads coming out on either side of the box and turning down in two parallel rows along the package. As integrated circuits became smaller and more complex, the number of leads coming out of the package increased, even though the package size remained the same or decreased. One solution to this problem was the flat, plastic leadless chip carrier (PLCC), which typically is a small, flat square package having the leads coming out and formed around each of the four edges of the package. As integrated circuits became even more complex, even the PLCC was inadequate to carry all the leads required without making the part unreasonably large.
The most recent solution to the problem of putting a large number of leads on a small package is the pin grid array (PGA). These packages are generally flat and square, but have a large number of leads coming out of the bottom of the package, parallel to each other, but perpendicular to the bottom of the package. The PGA packages can contain pin counts on the order of 100 in a 10.times.10 array or 169 in a 13.times.13 array or even larger.
As with each new innovation in package, a system had to be worked out for testing the integrated circuits in the new PGA packages. Because the PGA packages had the leads coming straight out of the package, a scheme had to be devised for perpendicularly inserting the PGA packages one by one into a test site which would make electrical contact with each of the leads and the circuit could be put through its paces by test software.
Current attempts at designing test sites for PGA parts have proved unsatisfactory. One commercial test site employs a test site box having a plurality of offset contact wires rising from the bottom of the box to the top of the open-ended box in a rectilinear pattern to correspond to and register with the lead pins from a PGA part. The ends of the upraised wire contacts are bent slightly and designed to meet with and be slightly sprung by tiny pegs on the underside of the lid of the test site. The lead pins on the PGA part then penetrate through holes in the test site lid and come into offset contact with the slightly bent tips of the upraised contact wires. The bottom ends of the contact wires are exposed through the bottom of the test site so that connection could be made to a customary device-under-test (DUT) board and eventual contact with the host test computer.
This test site configuration has many problems which include the fact that all of the wires are firmly fixed into the test site so that if one of the wires is damaged, the entire test site has to be removed for repair. Because the wires, which are cast into the test site, must be precisely aligned, such test sites are very costly to produce. Also, it is extremely easy to bend one of the contact wires and once bent, it is difficult by visual inspection to tell which wire is damaged or out of alignment. This problem has the related effect that the test site will sometimes reject PGA parts as "bad" when in fact the part is good but did not make contact with the offset wires. Further, because the test site lid pegs must make precise contact with the tips of the contact wires and spring them into proper alignment, it is particularly difficult to put the lid on the test site properly.